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Instruction: Which type of rock is the oldest on Earth?
Output:
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The oldest rocks on Earth are the igneous rocks that make up the Earth's mantle and crust, which are estimated to be around 4.4 billion years old. These rocks have been mostly recycled by plate tectonics and have been replaced by younger rocks over time. The oldest sedimentary rocks on Earth are estimated to be 3.8 billion years old, while the oldest metamorphic rocks are estimated to be 3.2 billion years old.